Influenza virus continues to be a major threat to human health. Current influenza virus vaccines aim to induce a strong antibody (Ab) response to the viral glycoproteins as these Abs are known to be highly protective when present at sufficient concentration in serum and respiratory tract secretions. The main problem inherent in these vaccines is that they target viral structures that are highly variable. Therefore, their effectiveness depends largely on the match between vaccine and epidemic virus strain and may be low or insignificant if the emergence of an epidemic virus strain with major alterations in its glycoproteins was not anticipated. This deficiency could be minimized by maximizing protective immune mechanisms that are broadly cross-reactive with virus strains within and between subtypes. A possible way to achieve this is through Abs directed to the ectodomain of the transmembrane protein M2 (M2e). M2e has remained highly conserved amongst human epidemic strains since 1918 to present. In the mouse model, M2e-specific Abs have been shown to be protective. Most importantly, limited evidence indicates that this response is poorly induced in humans by natural infection and current vaccines are not likely to induce it either. During the preceding granting period, we have shown that a synthetic multiple antigenic peptide (MAP) construct is effective in inducing M2e-specific Ab responses of high titer and long duration in the mouse model and for renewal, we propose to: 1) optimize the construct and immunization protocol to achieve maximum protection in the mouse model; 2) develop an ELISA for quantitative measurement of the M2e-specific Ab response in human sera; 3) investigate the propensity of influenza virus to escape anti-M2e Ab-mediated protection in vivo; and 4) study the protective activity of M2e-specific immunity in mouse models of severe pneumotropic and pantropic infections. These studies may provide better picture of the potential of M2e for human vaccination.